The complex interrelationships between cell surface membranes and differentiation will be investigated using differentiating skeletal muscle as a model system. Skeletal muscle differentiation in vitro, as well as in vivo proceeds through several stages culminating in the fusion of mononucleated myogenic cells into multinucleated myotubes which develop striations and become contractile. Since the cell surface or plasma membrane must play a key role in muscle differentiation, viz. cell recognition and cell fusion, we will examine in detail the surface membranes of cultured chick embryo muscle cells as a function of stage of differentiation. Various culture techniques will be utilized to synchronize the differentiation process and enrich cultures for cells at specific stages of differentiation. At each of these stages, plasma membranes will be isolated and the composition, metabolic turnover, and spatial distribution or topography of the membrane components will be compared. In addition, in conjunction with other studies in this laboratory on membrane development in genetically dystrophic muscle, primary differences between embryonic normal and dystrophic striated muscle will be sought. BIBLIOGRAPHIC REFERENCE: Schimmel, S.D. (1977) "Surface Labeling Studies of Normal and Genetically Dystrophic Myogenic Cells in Culture", Fed. Proc. (abstract in press).